A desiccant dehumidifier and a method performed by a control device for controlling a desiccant dehumidifier

Abstract

The disclosure relates to a desiccant dehumidifier (1) comprising: a desiccant rotor (2); a process air circuit (6) arranged to conduct a process airflow (8) of process air through a process sector (10) of the desiccant rotor (2); a regeneration air circuit (12) arranged to conduct a regeneration airflow (14) of regeneration air through a regeneration sector (16) of the desiccant rotor (2); a purge air circuit (18) arranged to conduct a purge airflow (20) of purge air through at least one purge sector (22) of the desiccant rotor (2), which purge air circuit (18) is fluidly connected to the regeneration air circuit (12) at a position in the regeneration air circuit (12) upstream of the desiccant rotor (2); and a regeneration air heater device (24), which is arranged in the regeneration air circuit (12) and is configured to heat the regeneration air in the regeneration airflow (14). A purge air heater device (26) is arranged in the purge air circuit (18), which purge air heater device (26) is configured to heat the purge air in the purge airflow (20).

Description

[0001] A desiccant dehumidifier and a method performed by a control device for controlling a desiccant dehumidifier

[0002] Technical field

[0003] The present invention relates to a desiccant dehumidifier comprising a desiccant rotor, which is rotatably arranged about a centre axis of the desiccant rotor; a process air circuit arranged to conduct a process airflow of process air through a process sector of the desiccant rotor; a regeneration air circuit arranged to conduct a regeneration airflow of regeneration air through a regeneration sector of the desiccant rotor; a purge air circuit arranged to conduct a purge airflow of purge air through at least one purge sector of the desiccant rotor, which purge air circuit is fluidly connected to the regeneration air circuit at a position in the regeneration air circuit upstream of the desiccant rotor; and a regeneration air heater device, which is arranged in the regeneration air circuit and is configured to heat the regeneration air in the regeneration airflow. The present invention also relates to a method performed by a control device, for controlling such a desiccant dehumidifier. Further, the present invention relates to a computer program stored on a computer-readable medium and also to a computer-readable medium having stored thereon the computer program.

[0004] Background art

[0005] Desiccant dehumidifiers, such as sorption dehumidifiers typically comprising a dehumidifying element in the form of a desiccant rotor or wheel holding desiccant material, which is effective in attracting and retaining water vapour. The desiccant rotor may be divided in two sectors, a process sector and a regeneration sector. The airflow to be dehumidified, process air, will pass through the process sector of the desiccant rotor, and the desiccant material in the rotor extracts moisture from the process air, so that it can leave the rotor as dried air. Simultaneously, the desiccant material is regenerated by another airflow, a regeneration airflow, which flows through the regeneration sector, all the while the desiccant rotor may rotate slowly about its centre axis. By means of the simultaneous dehumidification of the process air and the regeneration of desiccant material, the desiccant dehumidifier can be operated continuously.

[0006] US2007056307 discloses an example of a dehumidifier having a desiccant rotor. The air that flows through the regeneration sector is heated by a regeneration air heater device. The airflow through the regeneration sector may be generated by a fan. The heated air, which flows through the regeneration sector, releases humidity from the desiccant rotor and thus dries the rotor.

[0007] An even more effective regeneration process may be achieved if an additional airflow, a purge airflow, is used for regeneration of the desiccant material in the rotor and for recover heat generated by the regeneration air heater device.

[0008] Summary

[0009] The releasing of humidity from the desiccant rotor by regeneration air will reduce the humidity in the rotor, so that the desiccant rotor can extract moisture from the process air passing through the process sector. When the desiccant dehumidifier comprises a purge air circuit, the temperature of the mixture of regeneration air and purge air that flows through the desiccant wheel may be un-uniform due to the mixing of purge air into the regeneration air. An uncontrolled mixing of regeneration air and purge air may lead to an unstable and uncontrolled air temperature of the regeneration inlet sector of the desiccant rotor. An unstable air temperature results in that the air temperature may fluctuate several degrees. This unstable air temperature of the mixed regeneration air and purge air will affect the capacity of the desiccant dehumidifier negatively. The unstable temperature distribution profile of mixed regeneration air and purge air to the desiccant rotor may lead to energy inefficient regeneration of the desiccant rotor. This may be compensated for by increasing the energy from the heater, but this will increase the overall energy needs of the desiccant dehumidifier. The energy inefficient regeneration of the desiccant rotor may also be compensated for by arranging a separate mixing chamber for the regeneration air and purge air. However, such mixing chamber requires a large space and results in a large pressure drop for the regeneration air fan.

[0010] Therefore, it is a need for an improved desiccant dehumidifier and a method for controlling the desiccant dehumidifier, which stabilizes or increases the capacity of the desiccant dehumidifier.

[0011] There is a further need for an improved desiccant dehumidifier and a method for controlling the desiccant dehumidifier, in which the regeneration of the desiccant rotor is energy efficient. An objective of the present invention is to mitigate, alleviate or eliminate one or more of the above-identified deficiencies and disadvantages in the prior art and to solve at least the above-mentioned problem.

[0012] A further objective of the present invention is to achieve a desiccant dehumidifier and a method for controlling the desiccant dehumidifier, which stabilizes or increases the capacity of the desiccant dehumidifier.

[0013] A further objective of the present invention is to achieve a desiccant dehumidifier and a method for controlling the desiccant dehumidifier, in which the regeneration of the desiccant rotor is energy efficient.

[0014] These objectives are achieved by the desiccant dehumidifier initially defined, further comprising a purge air heater device arranged in the purge air circuit, which purge air heater device is configured to heat the purge air in the purge airflow. Further, these objectives are achieved by the method initially defined, comprising the step of: controlling the purge air heater device to provide a substantially stable temperature of a mixture of the regeneration air and the purge air, which mixture is configured to pass through the desiccant rotor. These objectives are also achieved by a computer program stored on a computer-readable medium initially defined, comprising instructions, which when the program is executed by a data processing unit of a control device of the desiccant dehumidifier, cause the control device to carry out the method. Further, these objectives are also achieved by the computer-readable medium having stored thereon the computer program.

[0015] According to a first aspect there is provided a desiccant dehumidifier comprising: a desiccant rotor, which is rotatably arranged about a centre axis of the desiccant rotor; a process air circuit arranged to conduct a process airflow of process air through a process sector of the desiccant rotor; a regeneration air circuit arranged to conduct a regeneration airflow of regeneration air through a regeneration sector of the desiccant rotor which purge air circuit is fluidly connected to the regeneration air circuit at a position in the regeneration air circuit upstream of the desiccant rotor; a purge air circuit arranged to conduct a purge airflow of purge air through at least one purge sector of the desiccant rotor; and a regeneration air heater device, which is arranged in the regeneration air circuit and is configured to heat the regeneration air in the regeneration airflow. A purge air heater device is arranged in the purge air circuit, which purge air heater device is configured to heat the purge air in the purge airflow. The purge air heater device may provide a substantially stable or equalized temperature of the mixture of the regeneration air and the purge air, which is configured to pass through the desiccant rotor. The stable temperature of the mixture of the regeneration air and the purge air results in that the temperature may fluctuate only a few degrees. The temperature of the mixture of regeneration air and purge air that flows through the desiccant rotor may be uniform and stable due to the purge air heater device arranged in the purge air circuit, since the purge air heater device is configured to heat the purge air in the purge airflow. Due to the purge air heater device a controlled mixing of regeneration air and purge air may be achieved, which leads to a stable and controlled air temperature of the regeneration inlet sector of the desiccant rotor. The stable air temperature of the mixed regeneration air and purge air will not affect the capacity of the desiccant dehumidifier negatively. Instead, the stable temperature distribution profile of the mixed regeneration air and purge air to the desiccant rotor may lead to energy efficient regeneration of the desiccant rotor. The regeneration air heater device together with the purge air heater device are configured to increase and equalize the temperature of the mix of regeneration air and purge air to the desiccant rotor. The heated regeneration air and the heated purge air may generate a stable or a substantially stable temperature of the mix of regeneration air and purge air to the desiccant rotor. The purge air circuit may be arranged to conduct purge air through the purge sector of the desiccant rotor, which purge air circuit is arranged in fluid communication with the process air circuit upstream of the desiccant rotor and to the regeneration air circuit upstream of the heater device.

[0016] The purge air heater device may be arranged in the purge air circuit downstream of the desiccant rotor. The purge airflow is configured to be directed through the purge sector. The purge airflow flowing through the purge sector may have a temperature, which is lower than the temperature of the regeneration airflow passing through the desiccant rotor. Thus, the purge airflow flowing through the purge sector will decrease the temperature of that part or sector of the desiccant rotor in which the regeneration airflow has passed through the desiccant rotor. Due to the increased temperature of the desiccant rotor by the regeneration airflow, the temperature of the air in the purge airflow will increase when it flows through the purge sector. However, the temperature of the purge air in the purge airflow may be lower than the temperature needed of the regeneration air in the regeneration airflow. Further, the temperature of the purge air in the purge airflow may fluctuate due to variations in temperature in the desiccant rotor.

[0017] The purge air circuit may be connected to the regeneration air circuit at a position downstream of the regeneration air heater device and upstream of the desiccant rotor. The purge airflow is configured to be directed through the purge sector. The purge airflow flowing through the purge sector may have a temperature, which is lower than the temperature of the regeneration airflow passing through the desiccant rotor. Thus, the purge airflow flowing through the purge sector will decrease the temperature of that part or sector of the desiccant rotor in which the regeneration airflow has passed through the desiccant rotor. Due to the increased temperature of the desiccant rotor by the regeneration airflow, the temperature of the air in the purge airflow will increase when it flows through the purge sector. The purge airflow with increased temperature is directed to the regeneration air circuit at the position downstream of the regeneration air heater device and upstream of the desiccant rotor. Directing the purge airflow to a position downstream of the regeneration air heater device may increase the efficiency of the desiccant dehumidifier comparing to a direction of the purge airflow to the regeneration air circuit to a position before the regeneration air heater device. Thus, the purge air circuit is arranged to direct the purge airflow to said position in the regeneration air circuit downstream of the regeneration air heater device and upstream of the desiccant rotor.

[0018] A regeneration air fan may be arranged in the regeneration air circuit, which regeneration air fan is configured to generate the regeneration airflow in the regeneration air circuit. The volume flow of the regeneration air through the desiccant rotor may be generated by controlling the speed of the regeneration air fan. The speed of the regeneration air fan may be constant. The speed of the regeneration air fan may be variable.

[0019] The regeneration air fan may be arranged downstream of the desiccant rotor. Arranging the regeneration air fan downstream of the desiccant rotor generates a negative pressure of the regeneration air in the regeneration air circuit. The regeneration air may thus pass the regeneration air heater device and the desiccant rotor with a negative pressure.

[0020] The regeneration air fan may be configured to generate the purge airflow in the purge air circuit. The volume flow of the purge air together with regeneration air through the desiccant rotor may be generated by the regeneration air fan. The volume flow of both the purge air and the regeneration air through the desiccant rotor may be generated by the speed of the regeneration air fan. The fan may be connected to the control device. Since the fan is arranged downstream of the desiccant rotor, a negative pressure may be generated by the fan in the regeneration and purge air circuits.

[0021] According to a second aspect there is provided a method, performed by a control device, for controlling the desiccant dehumidifier. The method comprises the step of: controlling the purge air heater device, based on the temperature of the regeneration air in the regeneration airflow downstream of the regeneration air heater device, to provide a substantially stable temperature of a mixture of the regeneration air and the purge air, which mixture is configured to pass through the desiccant rotor. The regeneration air, heated by the regeneration air heater device, may have a set point regeneration temperature. The set point regeneration temperature may be selected to a value which effectively regenerates the desiccant rotor. The temperature of the purge air is increased by the purge air heater device before the purge air is added to the regeneration airflow. The purge air may be heated in the purge air heater device to a temperature, which corresponds to the set point regeneration temperature of the regeneration air. Thus, the purge air heater device may provide a purge air temperature which results in a substantially stable or equalized temperature of the mixture of the regeneration air and the purge air, which mixture is configured to pass through the desiccant rotor. The stable temperature of the mixture of the regeneration air and the purge air results in that the temperature may fluctuate only a few degrees.

[0022] The step of controlling the purge air heater device may be preceded by the steps of: determining the temperature of the regeneration air in the regeneration airflow downstream of the regeneration air heater device; and determining the temperature of the purge air in the purge airflow downstream of the purge air heater device. Since there may be temperature variations of the heated regeneration air, the temperature of the regeneration air downstream of the regeneration air heater device is determined by the control device. In view of the determined temperature of the regeneration air, the purge air may be heated in the purge air heater device to a temperature which corresponds to the temperature of the heated regeneration air. Further, since there may be variations in the determined temperature of the purge air, the purge air heater device may be controlled to compensate for these variations and deliver purge air at a temperature that corresponds to the temperature of the regeneration air. Thus, the purge air heater device may provide a purge air temperature which results in a substantially stable or equalized temperature of the mixture of the regeneration air and the purge air, which mixture is configured to pass through the desiccant rotor. The desiccant dehumidifier may comprise a first temperature sensor arranged in the regeneration circuit upstream of the desiccant rotor. The first temperature sensor may be arranged in the regeneration circuit downstream of the regeneration air heater device and upstream of the position where the purge air circuit is fluidly connected to the regeneration air circuit. A second temperature sensor may be arranged in the purge air circuit downstream of the purge air heater device and upstream of the position where the purge air circuit is fluidly connected to the regeneration air circuit. The control device may be connected to the regeneration air heater device, the purge air heater device, the first temperature sensor and the second temperature sensor. The first temperature sensor may be configured to detect a signal corresponding to the temperature of the regeneration air in the regeneration airflow downstream of the regeneration air heater device. The detected signal of the first temperature sensor is received by the control device, which is configured to determine the regeneration air temperature. The second temperature sensor may be configured to detect a signal corresponding to the temperature of the purge air in the purge airflow downstream of the purge air heater device. The detected signal of the second temperature sensor is received by the control device, which is configured to determine the purge air temperature. The first and second temperature sensors may be replaced by a first and a second air flow sensor. Knowing the heating effect of the regeneration air heater device and the purge air heater device, the temperature of the regeneration air in the regeneration airflow downstream of the regeneration air heater device and the temperature of the purge air in the purge airflow downstream of the purge air heater device may be calculated. Alternatively, the first and second temperature sensors may be replaced by a single temperature sensor arranged in the regeneration air circuit at a position downstream of the position where the purge air circuit is fluidly connected to the regeneration air circuit and upstream of the desiccant rotor.

[0023] The present disclosure also relates to a computer program stored on a computer- readable medium and comprising instructions, which when the program is executed by a data processing unit of a control device of a desiccant dehumidifier, cause the control device to carry out the method according to the second aspect. The disclosure further relates to a computer-readable medium having stored thereon the computer program. The method may be comprised in pre-programmed software, which may be implemented into a production unit suitable for utilizing the method. The pre-programmed software may be stored in the control device. Alternatively, or in combination, the software may be stored in a memory or in a computer at a distance from the control device.

[0024] Brief of the

[0025] The above objects, as well as additional objects, features and advantages of the present disclosure, will be more fully appreciated by reference to the following illustrative and non-limiting detailed description of example embodiments of the present disclosure, when taken in conjunction with the accompanying drawings.

[0026] Fig. 1 schematically illustrates in a view of perspective, a desiccant dehumidifier according to an example; Fig. 2 schematically illustrates a desiccant dehumidifier, according to a further example;

[0027] Fig. 3 shows a flowchart of a method according to an example, and

[0028] Fig. 4 schematically illustrates a control device according to an example.

[0029] Detailed description

[0030] The present disclosure will now be described with reference to the accompanying drawings, in which preferred example embodiments of the disclosure are shown. The disclosure may, however, be embodied in other forms and should not be construed as limited to the herein disclosed embodiments. The disclosed embodiments are provided to fully convey the scope of the disclosure to the skilled person.

[0031] Figure 1 schematically illustrates in a view of perspective, a desiccant dehumidifier 1 according to an example. The desiccant dehumidifier 1 comprises a desiccant rotor 2, which is rotatably arranged about a centre axis 4 of the desiccant rotor 2. A process air circuit 6 is arranged to conduct a process airflow 8 of process air through a process sector 10 of the desiccant rotor 2. A process air fan 11 is arranged in the process air circuit 6 to generate the process airflow 8 of process air. A regeneration air circuit 12 is arranged to conduct a regeneration airflow 14 of regeneration air through a regeneration sector 16 of the desiccant rotor 2. A purge air circuit 18 is arranged to conduct a purge airflow 20 of purge air through at least one purge sector 22 of the desiccant rotor 2, which purge air circuit 18 is fluidly connected to the regeneration air circuit 12 at a position in the regeneration air circuit 12 which is upstream of the desiccant rotor 2. The purge air circuit 18 is fluidly connected to the regeneration air circuit 12 by a connection element 23, which is arranged at the position in the regeneration air circuit 12 upstream of the desiccant rotor 2. A regeneration air heater device 24 is arranged in the regeneration air circuit 12 and is configured to heat the regeneration air in the regeneration airflow 14. The regeneration air heater device 24 is arranged in fluid communication with the regeneration air circuit 12. A purge air heater device 26 is arranged in the purge air circuit 18, which purge air heater device 26 is configured to heat the purge air in the purge airflow 20. The purge air heater device 26 is arranged in fluid communication with the purge air circuit 18 downstream of the desiccant rotor 2. The purge air circuit 18 is fluidly connected to the regeneration air circuit 12 at a position in the regeneration air circuit 12 downstream of the regeneration air heater device 24 and upstream of the desiccant rotor 2. A regeneration air fan 28 is arranged in the regeneration air circuit 12. The regeneration air fan 28 is configured to generate the regeneration airflow 14 in the regeneration air circuit 12. The regeneration air fan 28 is arranged downstream of the desiccant rotor 2. The regeneration air fan 28 is configured to generate the purge airflow 20 in the purge air circuit 18.

[0032] Fig. 2 schematically illustrates a desiccant dehumidifier 1 according to a further example. In fig. 2, the desiccant rotor 2 comprises the process sector 10, the regeneration sector 16 and the purge sector 22. The process air circuit 6 is arranged to conduct the process air 8 through the process sector 10. The process air fan 11 is arranged in the process air circuit 6 to generate a flow of the process air 8 in the process air circuit 6. The regeneration air circuit 12 is arranged to conduct regeneration air 14 through the regeneration sector 16. The purge air circuit 18 is arranged to conduct purge air 20 through the purge sector 22. The regeneration air heater device 24 is arranged in the regeneration air circuit 12 and is configured to heat the regeneration air in the regeneration airflow 14. The purge air heater device 26 is arranged in the purge air circuit 18, which purge air heater device 26 is configured to heat the purge air in the purge airflow 20.

[0033] The desiccant dehumidifier 1 further comprises a first temperature sensor 30 arranged in the regeneration circuit upstream of the desiccant rotor 2. The first temperature sensor 30 is arranged in the regeneration circuit 12 downstream of the regeneration air heater device 24 and upstream of the position where the purge air circuit 18 is fluidly connected to the regeneration air circuit 12. A second temperature sensor 32 is arranged in the purge air circuit 18 downstream of the purge air heater device 26 and upstream of the position where the purge air circuit 18 is fluidly connected to the regeneration air circuit 12. A control device 200 is connected to the regeneration air heater device 24, the purge air heater device 20, the first temperature sensor 30 and the second temperature sensor 32.

[0034] In fig. 1 the process airflow 8 is directed in the same direction through the desiccant rotor 2 as the direction of the regeneration airflow 14. In fig. 2 the process airflow 8 is directed through the desiccant rotor 2 in a direction which is opposite to the direction of the regeneration airflow 14.

[0035] Fig. 3 shows a flowchart of a method according to an example. The method is performed by the control device 200, for controlling a desiccant dehumidifier 1. The method relates to the desiccant dehumidifier 1 disclosed in figures 1 and 2. The desiccant dehumidifier 1 thus comprises comprises the desiccant rotor 2, the process air circuit 6 arranged to conduct a process airflow 8 of process air through a process sector 10 of the desiccant rotor 2 The process air fan 11 arranged in the process air circuit 6 to generate the process airflow 8 of process air, the regeneration air circuit 12 arranged to conduct a regeneration airflow 14 of regeneration air through a regeneration sector 16 of the desiccant rotor 2, the purge air circuit 18 arranged to conduct a purge airflow 20 of purge air through at least one purge sector 22 of the desiccant rotor 2, which purge air circuit 18 is fluidly connected to the regeneration air circuit 12 at a position in the regeneration air circuit 12 upstream of the desiccant rotor 2, the regeneration air heater device 24 arranged in the regeneration air circuit 12, which is configured to heat the regeneration air in the regeneration airflow 14, the regeneration air heater device 24 arranged in fluid communication with the regeneration air circuit 12, the purge air heater device 26 arranged in the purge air circuit 18, which purge air heater device 26 is configured to heat the purge air in the purge airflow 20, and the regeneration air fan 28 is arranged in the regeneration air circuit 12.

[0036] The method comprises the step of controlling slOl the purge air heater device 26, based on the temperature of the regeneration air in the regeneration airflow 14 downstream of the regeneration air heater device 14, to provide a substantially stable temperature of a mixture of the regeneration air and the purge air, which mixture is configured to pass through the desiccant rotor 2.

[0037] The step of controlling slOl the purge air heater device 26 is preceded by the steps of: determining sl02 the temperature of the regeneration air in the regeneration airflow 14 downstream of the regeneration air heater device 24; and determining sl03 the temperature of the purge air in the purge airflow 20 downstream of the purge air heater device 26. The first temperature sensor 30 is configured to detect a signal corresponding to the temperature of the regeneration air in the regeneration airflow 14 downstream of the regeneration air heater device 24. The detected signal of the first temperature sensor 30 is received by the control device 200, which is configured to determine the regeneration air temperature. The second temperature sensor 32 is configured to detect a signal corresponding to the temperature of the purge air in the purge airflow 20 downstream of the purge air heater device 26. The detected signal of the second temperature sensor 32 is received by the control device 200, which is configured to determine the purge air temperature.

[0038] Fig. 4 schematically illustrates a control device 200 of a desiccant dehumidifier 1 according to an example. The control device 200 comprises at least one data processing unit 201 and a computer-readable medium 202. The control device 200 may be configured to perform the method as described in fig. 3 upon execution of a computer program P by the at least one data processing unit 201. The computer program P comprises computer-readable instructions that may be stored in the computer-readable medium 202, such as a non- transitory hardware memory device of the control device 200.

Claims

CLAIMS1. A desiccant dehumidifier (1) comprising: a desiccant rotor (2), which is rotatably arranged about a centre axis (4) of the desiccant rotor (2); a process air circuit (6) arranged to conduct a process airflow (8) of process air through a process sector (10) of the desiccant rotor (2); a regeneration air circuit (12) arranged to conduct a regeneration airflow (14) of regeneration air through a regeneration sector (16) of the desiccant rotor (2); a purge air circuit (18) arranged to conduct a purge airflow (20) of purge air through at least one purge sector (22) of the desiccant rotor (2), which purge air circuit (18) is fluidly connected to the regeneration air circuit (12) at a position in the regeneration air circuit (12) upstream of the desiccant rotor (2); and a regeneration air heater device (24), which is arranged in the regeneration air circuit (12) and is configured to heat the regeneration air in the regeneration airflow (14), characterized in that a purge air heater device (26) is arranged in the purge air circuit (18), which purge air heater device (26) is configured to heat the purge air in the purge airflow (20).

2. The dehumidifier (1) according to claim 1, wherein the purge air heater device (26) is arranged in the purge air circuit (18) downstream of the desiccant rotor (2).

3. The dehumidifier (1) according to any one of the claims 1 and 2, wherein the purge air circuit (18) is fluidly connected to the regeneration air circuit (12) at a position in the regeneration air circuit (12) downstream of the regeneration air heater device (24) and upstream of the desiccant rotor (2).

4. The dehumidifier (1) according to any one of the preceding claims, further comprising a regeneration air fan (28) arranged in the regeneration air circuit (12), which regeneration air fan (28) is configured to generate the regeneration airflow (14) in the regeneration air circuit (12).

5. The dehumidifier (1) according to claim 4, wherein the regeneration air fan (28) is arranged downstream of the desiccant rotor (2).

6. The dehumidifier (1) according to any one of the claims 4 and 5, wherein the regeneration air fan (28) is configured to generate the purge airflow (20) in the purge air circuit (18).

7. A method, performed by a control device (200), for controlling a desiccant dehumidifier (1) according to any one of the preceding claims, the method is characterized by the step of: controlling (slOl) the purge air heater device (26), based on the temperature of the regeneration air in the regeneration airflow (14) downstream of the regeneration air heater device (24), to provide a substantially stable temperature of a mixture of the regeneration air and the purge air, which mixture is configured to pass through the desiccant rotor (2).

8. The method according to claim 7, wherein the step of controlling (slOl) the purge air heater device (26) is preceded by the steps of: determining (sl02) the temperature of the regeneration air in the regeneration airflow (14) downstream of the regeneration air heater device (24); and determining (sl03) the temperature of the purge air in the purge airflow (20) downstream of the purge air heater device (26).

9. A computer program (P) stored on a computer-readable medium (202) and comprising instructions, which when the program (P) is executed by a data processing unit (201) of a control device (200) of a desiccant dehumidifier (1), cause the control device (200) to carry out the method according to any one of the claims 7 and 8.

10. A computer-readable medium (202) having stored thereon the computer program (P) of the claim 9.

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